When we solve by elimination, we're essentially "eliminating" a variable so that we can solve for other more easily. Here, let's eliminate the y variable by adding the two equations together:
6x + 2y = 18
+ -4x - 2y = -6
____________
2x + 0y = 12
x = 12/2 = 6
Plug this back into one of the original equations to find y: